Treatment of slags



Patented Mar. 27, 1951 UNITED STATES r TREATMENT OF SLAGS James C.Vignos, Canton, Ohio, assignor to Ohio Form-Alloys Corporation, Canton,Ohio, a corporation of Ohio No Drawing. Application June 2, 149, SerialNo. 96,823

5 Claims.

This invention relates to the treatment of slags and more particularlyto the removal of phosphorus from slags resulting from iron and,

steelmaking operations. This application is a continuation-in-part of myapplication, Serial No. 606,873, filed July 24, 1M5, now abandoned.

In the production of iron and steel of any desired quality from theusual wide range of raw materials such iron and steel scrap, pig iron(cold or molten), it is necessary to remove the impurities, usuallycarbon, phosphorus. silicon, manganese, chromium, etc. These impuritiesare ordinarily removed by oxidation with air or metallic oxides such asiron ore, manganese ore, chrome ore, etc., depending upon the processand the impurities to be removed. Such oxidation procedures place theresulting impurity oxides in suitable slag which is readily removed orseparated from the molten metal. This slag con tains the major portionof the sulfur, phosphorus,

mangansse and silicon of the original charge in the form of oxides asWell as a considerable proportion of iron oxide.

Various methods have been suggested for treating the molten steelmalringsiege to reduce the iron and manganese oxides, such as reduction withcarbonaceous reducing agents or with noncarbonaceous reducing agents bya variety of methods. Such slags are a potentially rich source ofmanganese in particular. However, the suggested methods of salvagingmanganese are so unsatisfactory that its recovery from these slags hasnot been economically feasible because in reducing the manganese oxidesthe iron, sulfur and phosphorus oxides are likewise redued and theresulting metal is too high in phosphorus to find commercialapplication.

It has been my experience that the reduction of such slags and theremoval of phosphorus can not be economically carried out in a refiningfurnace. Such methods of reduction as have been proposed are thereforeeconomically undesirable and generally unsatisfactory in that thephosphorus must be subsequently removed from the metal by furtherrefining processes. It has also been my experience that a reductionprocess using carbonaceous materials produces a reaction so endothermicin character that it must be carried out in a furnace. This requires theuse of expensive equipment and has to a considerable extent preventedthe recovery of manganese from slags.

I have discovered that the answer to the problem of manganese recoveryfrom slags is to be found in fractionally separating the phosphorus fromthe slag as an iron-phosphorus alloy under certain conditions which Ishall hereafter describe then separating the manganese, in stead ofreducing the combined oxides of phosphorus, sulfur, iron, manganese,etc, and then attempting to separate the phosphorus from the resultingalloy.

I have found a method of fractionally sepcrating phosphorus from moltenslag outside of a furnace by the addit'on of a reducing agent which whenadded to the slag will react with the slag to maintain it in the moltencondition and at the same time cause substantially continuous agitationof the slag during its reaction therewith and will, if added in theproper amounts, reduce the phosphorus oxide and suflicient iron oxide tocombine with the phosphorus in the form of an iron-phosphorus alloywhich may be readily separated from the remaining manganese oxidecontaining material. Most efiicient separation may be had thecomposition of the iron-phosphorus alloy has a melting point at or belowthe melting point of the slag. Preferably the composition of my reducingagent is adjusted-so that it not only maintains the slag in the moltencondition but also substantially maintains the thermodynamic balance ofthe slag. The remaining manganese oxide containing material may then betreated by any of the known reduction. methods to produce satisfactorymanganese alloy.

A reducing agent which I have found tohave the aforementioned requiredproperties and to be most effective in my method is a mixture ofcarbonaceous and noncarbonaceous materials, preferably a mixture ofcarbonaceous material such as coke breeze and ferro-silicon. Ordinarilya mixture of about 40% carbonaceous material and noncarbonaceousmaterial will form a "satisfactory reducing agent although theseproportions may vary depending upon the composition of the slag and thenature of both the carbonaceous and noncarbonaceous material. Undercertain conditions I have used as little as 5% carbonaceous reducingagent combination with noncarbonaceous reducing agent but generally theproportion of carbonaceous material should be larger. While prefer touse ferro-silicon as the non-carbonaceous reducing agent, othernoncarbonaceous reducing agents including aluminum, magnesium, calcium,and titanium and their alloys may be used.

A. starter or initiator, such as sodium nitrate or other oxidant, may beadded to the mixture to accelerate the reaction.

Example I As an example of the process of my invention, 10 net tons offlush-off slag having the following composition,

Percent C310 2 M O 5.5 A1203 2 P205 1.5

were treated with 1000 pounds of coke breeze, 1800 pounds of 77%ferro-silicon and 200 pounds of sodium nitrate as it flowed from thefurnace into a ladle. An energetic reaction ensued during which the slagwas continually agitated by the reaction and also remained in asatisfactory physical condition, 1. e., it did not cool and solidify nordid it become overheated, wild and uncontrollable upon the addition ofthe treating materials. After the energetic reaction was completed, theiron-phosphorus alloy was tapped from the bottom of the ladle. Analysisof the approximately 5300 pounds of metal thus produced showed about2.26% phosphorus, or about 90% of the phosphorus originally in the slag.

Example II In this example it was desired to remove about 90% of theiron along with the phosphorus in a flush-off slag having a compositionsimilar to that of Example I. A net ton of molten slag was treatedwith83 pounds of coke, 2410 pounds of 75% ferro-silicon and pounds ofsodium nitrate to produce a metal having the following analysis:

Analysis of the remaining manganese rich slag showed it to contain only0.13% P205.

Example III A net ton of slag similar to the composition of the slag ofExample I wastreated with a mixture of 10 pounds of coke and 177 poundsof 74% ferro-silicon. The resulting 500 pounds of metal contained 2.2%phosphorus or approximately 80% of the phosphorus in the slag andmetallic iron equivalent to about 70% of the iron oxide in the slag.

While I have illustrated and described a present preferred practice ofmy invention, it will be understood that it may be otherwise embodiedwithin the scope of the following claims.

I claim:

1. A process for removing phosphorus from slags containing phosphorus,manganese and iron oxides outside of a furnace to produce asubstantially phosphorus-free manganese oxide containing material fromwhich manganese may be recovered by known 'means which comprisestreating the slag in the molten condition with a sufrlcient amount of amixture of about 5% to 40% carbonaceous reducing agents and about 95% tononcarbonaceous reducing agents to reduce the greater part of thephosphorus oxide and sufi'icient iron oxide to combine with thephosphorus in the form of an iron-phosphorus alloy and separating theiron-phosphorus alloy from the remaining manganese oxide containingmaterial.

2. A process for removing phosphorus from slags containing phosphorus,manganese and iron oxides outside of a furnace to produce asubstantially phosphorus-free manganese oxide cona concentration in themetal of l taining material from which manganese may be recovered byknown means which comprises treating the slag in the molten conditionwith a sufficient amount of a mixture of about 40% carbonaceous reducingagents and about 60% noncarbcnaceous reducing agents'to reduce thegreater part of the phosphorus oxide and sufficient iron oxide tocombine with the phosphorus in the form of an iron-phosphorus alloy andeparating the iron-phosphorus alloy from the remaining manganese oxidecontaining material.

3. A process for removing phosphorus from slags containing phosphorus,manganese and iron oxide outside of a furnace to produce a substantiallyphosphorus-free manganese oxide con taining material from whichmanganese may be recovered by known means which comprises treating theslag in the molten condition with a sufficient amount of a mixture ofabout 40% carbonaceous reducing agents, about 60% noncarbonaceousreducing agents, combined with an oxidant starter to reduce the greaterpart of the phosphorus oxide and sufficient iron oxide to combine withthe phosphorus in the form of an iron-phosphorus alloy and separatingthe iron phosphorus alloy from the remaining manganese oxide containingmaterial.

a. A process for removing phosphorus from slags containing phosphorus,manganese and iron oxides outside of a furnace to produce asubstantially phosphorus-free manganese oxide containing material whichcomprises treating the slag in the molten condition with a mixture ofcarbonaceous and noncarbonaceous reducing agents in such proportionsthat the molten condition of the slag is maintained and a substantiallycontinuous agitation of the slag is maintained during its reactiontherewith, said mixture being added in sufficient quantity to reduce thegreater part of the phosphorus oxide and at least sufficient iron oxideto combine with the phosphorus in the form of an iron-phosphorus alloyand separating the iron-phosphorus alloy from the remaining slag.

5. A process for removing phosphorus from slags containing phosphorus,manganese, and

iron oxides outside of a furnace to produce a substantiallyphosphorus-free manganese oxide containing material which comprisestreating the slag in the molten condition with a mixture of carbonaceousand non-carbonaceous reducing agents and an oxidant starter in suchproportions that the molten condition of the slag is maintained and asubstantially continuous agitation of the slag is maintained during itsreaction therewith, said mixture being added in sufiicient quantity toreduce the greater part of the phosphorus oxide and at least sufficientiron to combine with the phosphorus in the form of an ironphosp-horusalloy and separating the iron-phosphorus alloy from the remaining slag.

JAMES C. VIGNOS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 905,281 Betts Dec. 1, 19081,028,070 I-Iiorth May 28, 1912 2,350,725 Cavanagh June 6, 19442,471,562 Fitterer May 31, 1949

1. A PROCESS FOR REMOVING PHOSPHORUS FROM SLAGS CONTAINING PHOSPHORUS,MANGANESE AND IRON OXIDES OUTSIDE OF A FURNACE TO PRODUCE ASUBSTANTIALLY PHOSPHORUS-FREE MANGANESE OXIDE CONTAINING MATERIAL FROMWHICH MANGANESE MAY BE RECOVERED BY KNOWN MEANS WHICH COMPRISES TREATINGTHE SLAG IN THE MOLTEN CONDITION WITH A SUFFICIENT AMOUNT OF A MIXTUREOF ABOUT 5% TO 40% CARBONACEOUS REDUCING AGENTS AND ABOUT 95% TO 60%NONCARBONACEOUS REDUCING AGENTS TO REDUCE THE GREATER PART OF THEPHOSPHORUS OXIDE AND SUFFICIENT IRON OXIDE TO COMBINE WITH THEPHOSPHORUS IN THE FORM OF AN IRON-PHOSPHORUS ALLOY AND SEPARATING THEIRON-PHOSPHORUS ALLOY FROM THE RRMAINING MANGANESE OXIDE CONTAININGMATERIAL.